A tire comprising a crown comprising a crown reinforcement surmounted by a tread is known from the prior art. Two sidewalls extend the crown radially inwards. The tire comprises two beads radially on the inside of the sidewalls and each comprising an annular reinforcing structure. The annular reinforcing structure comprises a bead wire substantially of revolution about an axis comprising several windings of at least one wire which are arranged axially next to one another over several layers radially superposed on one another. The wire has a substantially circular cross section. Such a bead wire is generally referred to as a round bead bundle. The bead wire of the prior art, illustrated in FIG. 9, may be bare or encased in a mass of encasing rubber.
The tire also comprises a radial carcass reinforcement extending from the beads to the sidewalls towards the crown. The carcass reinforcement comprises one or more carcass plies, at least one of these carcass plies being anchored in each of the beads by being folded around the annular reinforcing structure, in contact with the bead wire or the encasement thereof, so as to form, within each bead, a main strand extending radially between each bead through the sidewalls and the crown and a turnup extending radially from each bead through each sidewall.
Each bead comprises a mass of filling rubber arranged in contact with the bead wire or the encasement thereof, in a space delimited by the main strand and turnup. Each bead also comprises additional masses of rubber arranged axially on the outside of the turnup.
During the manufacture of the tire of the prior art, which is performed for example on a tire-building drum, the bead wire is placed on the carcass ply and the turnup is folded around the bead wire. The carcass ply and the bead wire are then turned relative to one another. During this rotation, the mass of filling rubber and the folding of the carcass ply comprising the main strand and the turnup rub against the bead wire or the encasement thereof, thereby creating what is referred to as a braking torque that prevents the relative rotation of the bead wire with respect to the rest of the tire, notably with respect to the carcass ply.
The braking torque causes the turnup of the carcass ply and the additional masses of rubber arranged axially on the outside of the turnup to be placed in compression. The braking torque also causes the main strand of the carcass ply to be placed in overtension. Under the effect of the overtension in the main strand, the windings of the bead wire, notably the windings in contact with the overtensioned main strand become disorganized. In addition, the friction leads to limited relative rotation which prevents the bead wire from adopting a correct orientation within the tire.
When they occur, these potential problems, which have been deliberately exaggerated in FIG. 10, cause the tire to have to be scrapped.